Sinha was serving as the Principal Advisor to Prime Minister Modi since September 2019. Before assuming the role, he had served as the Cabinet Secretary for four years.

PK Sinha, one of the most senior bureaucrats in the Narendra Modi-led government, has resigned on personal grounds, sources claimed on March 16.
A 1977-batch IAS officer of Uttar Pradesh cadre, Sinha was serving as the Principal Advisor to Prime Minister Modi since September 2019. Before assuming the role, he had served as the Cabinet Secretary for four years.
In the previous United Province Alliance (UPA)-led government, Sinha served as a secretary in three central ministries. After Modi took over as the prime minister in 2014, Sinha was retained as the Power Secretary.
In the first year of the Modi government – when Sinha was the top bureaucrat in the Union power ministry – the country had recorded 22,566 MW capacity addition and the highest ever increase in the transmission line.
In June 2015, Sinha was appointed as the Cabinet Secretary. After his term was due in June 2019, he was provided a third extension, making him the longest serving Cabinet Secretary. In September that year, he replaced retiring bureaucrat Nripendra Misra in the PMO.
After Misra, Sinha is considered as the tallest bureaucrat to leave the PMO after the 2019 Lok Sabha polls. Both the retired IAS officers were also considered as two among the most trusted officials in the Prime Minister’s Office.